William J. DeSisto Associate Professor   • B.S. University of Rhode Island, 1986 • Ph.D. Brown University, 1989   Phone: 207-581-2291 Fax: 207-581-2323 Email: wdesisto@umche.maine.edu

Research Interests

Inorganic membrane synthesis and characterization • application of chemical vapor deposition and atomic layer deposition to membrane synthesis • filtration for microdevices • selective adsorption materials synthesis and characterization

Current Research

My research is currently focused on new materials and synthetic routes for inorganic membranes and the surface modification of nanoparticles. The ceramic membrane research has focused on microstructural control of pore size and porosity as well as surface functionalization to tailor adsorptive properties. These new membranes and nanoparticles may open up new applications in gas separations, gas separation and reaction, and in Li-ion transport in solid-state secondary batteries. Particular gas separation applications include on-site natural gas purification, carbon dioxide separation for sequestration and nitric oxide removal from cigarette smoke. Improved energy conversion devices will impact our country’s ability to combat terrorism and also open up unique applications in healthcare, where non-toxic batteries are needed. Since coming to Maine, I have performed both government and industrial sponsored research.

Pore Size Reduction of Mesoporous Silica Membranes Using Catalyzed Atomic Layer Deposition of Silicon Dioxide

There is a current pore size “gap” in silica membranes that lies between dense membranes (pore diameter ~5Å) and mesoporous membranes (pore diameter ~20-100Å). New synthesis strategies are needed to prepare silica membranes with controlled pore size in the 5-20Å range. Our approach involves using catalyzed atomic layer deposition (C-ALD) of silicon dioxide in a silica mesoporous matrix where the catalyst acts as a template to define the final pore size of the membrane. C-ALD of SiO₂ takes place in the silica mesoporous matrix using SiCl₄ and H₂O as reactants, and amines or ammonia as a catalyst. SiO₂ forms within the mesoporous silica using two sequential half-reactions, each of which is surface-limited. The first reaction (A) is the surface-catalyzed attachment of SiCl₄. The second reaction (B) is the hydrolysis of SiCl₄ to SiO₂, completing the reaction cycle and resulting in one monolayer of SiO₂ formation. Repeated ABAB cycles results in the pore size reduction of the mesoporous silica membrane. At the point of catalyst exclusion from the pore, the reaction cycles self-terminate, resulting in a specific pore size of the membrane. Since the SiCl₄ attachment is catalyzed by tertiary amines, aromatic amines and ammonia, several catalysts of various sizes can be used in the SiO₂ deposition effectively tuning final pore size. In addition, we are pursuing an understanding of the reaction thermodynamics and kinetics that will allow the confinement of the pore-size reduction to the surface of the mesoporous layer, maximizing flux through the membrane. The self-limiting reaction may also find application in the ever-present membrane problem of defect repair. A figure of the catalyst-controlled pore size reduction of a silica membrane is shown below.

Inorganic Membranes for CO₂/N₂ Separation

In order to comply with federal emission standards the energy and chemical processing industries have been steadily reducing CO₂ emissions for the last 10 years. Carbon dioxide scrubbing, using a caustic absorber column, is the most common way to reduce industrial CO₂ emissions. Both polymeric and inorganic membranes show promise for the separation of CO₂ from N₂. Porous inorganic membranes provide thermal and chemical stability over polymeric membranes and are therefore the most likely candidate for large scale industrial application. A successful CO₂/N₂ separation will enable efficient carbon sequestration via reaction with magnesium silicates, for example.

The overall objective of research in inorganic membranes for gas separations is the controlled synthesis and production of thermally stable, defect-free supported films, with a perfect control of the microstructure (pore size, pore volume and surface area). Once this objective is met, inorganic membranes can be tailored for CO₂/N₂ separation by functionalizing the pore walls to enhance adsorption and surface diffusion of the CO₂ molecule.

A state-of-the-art thin, mesoporous layer deposited within the pores of a macroporous a-Al₂O₃ support is chemically modified to attain a uniform and controlled pore-structure. Pore size reduction of the mesoporous matrix is achieved by using a catalyzed binary reaction sequence, referred to as atomic layer deposition. Once a monodisperse pore size is attained a final modification step is employed to functionalize the internal pore walls with aminopropyl groups in order to enhance sorption and surface diffusion of CO₂. Membranes are characterized for gas transport and separation of CO₂/N₂ gas mixtures. The membrane performance is related to membrane microstructure and surface chemistry. Molecular modeling calculations are used to physically describe the amino-CO₂ interaction aiming to optimize facilitated transport of CO₂ through the membrane. Below is a figure showing the membrane architecture.

Atomic Layer Deposition of Nitrides on Nano-particles for Enhanced Energy Conversion to Combat Terrorism

Novel breakthroughs in energy conversion technology are urgently needed to push technology beyond incremental improvements in performance and into the next generation of high energy density, compact devices. This research focuses on passivating nano-particle surfaces, with the potential to impact broad areas of research including nano science and technology and energy conversion devices. Despite research progress, the insertion of nano-materials as electrodes in, for example, lithium-ion batteries, has been limited because of the extreme reactivity of the nano-particles with high surface areas. Initial experiments are focused on coating nano-sized lithium-ion battery anodes with titanium nitride using atomic layer deposition. The overall chemical reaction is shown below.

3TiCl₄ + 4NH₃ ® 3TiN + 12HCl + ½N₂

This reaction will also be broken down into two successive reaction schemes. First the oxide nano-particle surface will be exposed to TiCl₄ at 400°C, followed by an inert gas purging. Second, the TiCl* surface species will be exposed to NH₃ at 400°C. This will produce one monolayer of TiN

Fundamental studies of the reaction chemistry, particularly in the first several layers of the deposition process will be carried out using in-situ FTIR experiments and Raman spectroscopy. Coin cell batteries will be fabricated, tested and evaluated for overall energy density, rate capability, etc.

This project involves a collaboration with Yardney Technical Products, Inc. a manufacturer of Li-ion batteries. The anodes will be passivated at the University of Maine and batteries will be fabricated and evaluated at Yardney/Lithion Technical Products, Inc., through an ongoing, highly productive collaboration between the PI and industry.

Silica Membranes for Separator/Electrolytes in Li-ion Batteries

Plastic separators currently used in Li-ion batteries breakdown at mild temperatures creating an electrical short between the anode and cathode. This fact, coupled with the use of an organic solvent and of course, Li salts that are highly reactive in air, create serious safety issues for the industry. Through a collaboration with Yardney Technical Products, Inc. we are investigating silica/polymer composite separators to improve safety and also give us insight into potential solid state separator/electrolyte systems. We are currently preparing mesoporous silica membranes via surfactant templating techniques to control pore size and porosity. We are investigating the use of both cationic and neutral surfactants in the synthesis. In addition, we are investigating the synthesis of mesoporous zirconia membranes via surfactant templating.

Materials for Selective NO and CO Adsorption

Through a collaboration with Philip Morris USA, we are investigating novel materials for the removal of NO and CO from cigarette smoke. Examples of materials include hemoglobin and myoglobin encapsulated in silica gels and powders. Protein encapsulated powders were fabricated via the condensation of silicic acid around the protein, followed by a fast freezing with liquid nitrogen, and subsequent thawing. The fast freezing technique led to high surface area stable silica encapsulated protein powders. Transmission UV-Vis spectroscopy techniques were used to verify that neither protein was damaged during gelling or freezing processes. Both hemoglobin and myoglobin gels and powders retained their biological activity and were able to bind cyano ligands while in the oxidized Fe⁺³ state and carbon monoxy ligands while in the reduced Fe⁺² state. Kinetics experiments showed that the rates of binding of CO and CN^- to the proteins in the silica gel versus a buffer solution are decreased by 30-45%. This result was likely due to mass transfer effects associated with diffusion through the gel network. Hemoglobin/silica powders were successfully stabilized in the Fe⁺² oxidation state by addition of the amino acid L-cysteine. An example of powders with varying concentrations of myoglobin are shown below.

Selected Publications

B.A. McCool and W.J. DeSisto, “Self-limited pore size reduction of mesoporous silica membranes via pyridine-catalyzed silicon dioxide ALD,”  accepted for publication in Advanced Materials (Chemical Vapor Deposition).

B.A. McCool and W.J. DeSisto, “Synthesis and characterization of silica membranes prepared by pyridine-catalyzed atomic layer deposition,”  Ind. Eng. Chem. Res., 43, 2478 (2004).

B.A. McCool, R.A. Cashon, G. Karles, and W.J. DeSisto, “Silica encapsulated hemoglobin and myoglobin powders prepared by an aqueous fast-freezing technique,” Journal of Non-Crystalline Solids, 333, 143 (2004).

B.A. McCool, N. Hill, J. DiCarlo, and W.J. DeSisto, “Synthesis and characterization of mesoporous silica membranes via dip-coating and hydrothermal deposition techniques,” Journal of Membrane Science, 218, 55 (2003).

Young-Nam Cho and William DeSisto, “Phase-selective CVD of chromium oxides from chromyl chloride,” Advanced Materials (Chemical Vapor Deposition), 9, 119 (2003).

V.M. Bermudez and W.J. DeSisto, “Study of chromium oxide film growth by chemical vapor deposition using infrared reflection absorption spectroscopy,” Journal of Vacuum Science and Technology A, 19(2), 576 (2001).

M.S. Osofsky, B. Nadgorny, R.J. Soulen, Jr., G. Trotter, P. Broussard, W. DeSisto, G. Laprade, Y.M. Mukovskii, and A. Arsenov, “Measurement of the transport spin-polarization of oxides using Point Contact Andreev Reflection (PCAR),” Physica C, 341-348, 1527 (2000).

W.J. DeSisto, P. Broussard, T. Ambrose, B. Nadgorny, and M. Osofsky, “Highly spin-polarized chromium dioxide thin films prepared by chemical vapor deposition from chromyl chloride,” Applied Physics Letters, 76, 3789 (2000).

E.J. Cukauskas, J.M. Pond, E.A. Dobisz, and W.J. DeSisto, “Critical current characteristics of YBa₂Cu₃O₇ thin films on (110) SrTiO₃,” Applied Superconductivity, 10, 1649 (2000).

J. Grun, R.P. Fischer, M. Peckerar, C.L. Felix, B.C. Covington, W.J. DeSisto, D.W. Donnelly, A. Ting, and C.K. Manka, “Athermal annealing of phosphorus-ion-implanted silicon,” Applied Physics Letters, 77, 1997 (2000).

W.J. DeSisto, E.J. Cukauskas, B.J. Rappoli, J.C. Culbertson, and J.H. Claassen, “Metal-Organic chemical vapor deposition of La₂CuO_4+x thin films with gas phase composition control,” Chemical Vapor Deposition, 5, 233 (1999).

E.J. Cukauskas, S.W. Kirchoefer, W.J. DeSisto, and J.M. Pond, “Ba_(1-x)Sr_xTiO₃ thin films by off-axis cosputtering of BaTiO₃ and SrTiO₃,” Appl. Phys. Lett., 74, 4034 (1999).

D.D. Koleske, A.E. Wickenden, R.L. Henry, W.J. DeSisto, and R.J. Gorman, “Growth model for GaN with comparison to structural, optical, and electrical properties,” J. Appl. Phys., 84, 1998 (1998).

W.J. DeSisto and B,J. Rappoli, “Ultraviolet absorption sensors for precursor delivery rate control for metalorganic chemical vapor deposition of multiple component oxide thin films,” J. Crystal Growth, 191, 290 (1998).

D.D. Koleske, A.E. Wickenden, R.L. Henry, W.J. DeSisto, and R.J. Gorman, “A Kinetic Model for GaN Growth,” 1997 Fall MRS Symposium Proceedings.

B.J. Rappoli, W.J. DeSisto , T.J. Marks, and J.A. Belot, “MOCVD precursor delivery monitored and controlled using UV spectroscopy,” Mat. Res. Soc. Symp. Proc., 1997 (in press).

W.J. DeSisto and B.J. Rappoli, “In-line UV spectroscopy of YBa2Cu3O7 MOCVD precursors, J. Crystal Growth, 170, 242 (1997).

B.J. Rappoli and W.J. DeSisto, “MOCVD HTSC precursor delivery monitored by UV spectroscopy,” Materials Research Society Symposium Proceedings, Vol. 415, 149 (1996).

B.J. Rappoli and W.J. DeSisto, “Gas phase ultraviolet spectroscopy of high-temperature superconductor precursors for chemical vapor deposition processing,” Applied Physics Letters, 68 (19), 2726 (1996).

W.J. DeSisto, E.S. Snow, and C.L. Vold, “Metalorganic chemical vapor deposition of YBCO thin films on (100) MgO,” J. Crystal Growth, 154, 68 (1995).